Electrical Frequency Response Research Articles

KLT-Based Interrogation Technique for FBG Multiplexed Sensor Tracking

The Karhunen–Loeve transform (KLT) is used to retrieve the wavelength information of several fiber Bragg gratings (FBGs) that are acting as a multiplexed sensor. The modulated light of a broadband source is launched to the FBG cascade in order to capture the electrical frequency response of the system. Thanks to dispersive media, the wavelengths of the FBGs are mapped in radio-frequency delays. Wavelength changes are determined by the amplitude change of the samples in the impulse response, a change which is followed by the eigenvalue calculated by the KLT routine. The use of the KLT routine reduces by three orders of magnitude the amount of points needed to have a subdegree resolution in temperature sensing, while keeping the accuracy almost intact.

Direct electrical and mechanical characterization of in situ generated DNA between the tips of silicon nanotweezers (SNT).

Previously, we reported the application of micromachined silicon nanotweezers (SNT) integrated with a comb-drive actuator and capacitive sensors for capturing and mechanical characterization of DNA bundles. Here, we demonstrate direct DNA amplification on such a MEMS structure with subsequent electrical and mechanical characterization of a single stranded DNA (ssDNA) bundle generated between the tips of SNT via isothermal rolling circle amplification (RCA) and dielectrophoresis (DEP). An in situ generated ssDNA bundle was visualized and evaluated via electrical conductivity (I-V) and mechanical frequency response measurements. Colloidal gold nanoparticles significantly enhanced (P < 0.01) the electrical properties of thin ssDNA bundles. The proposed technology allows direct in situ synthesis of DNA with a predefined sequence on the tips of a MEMS sensor device, such as SNT, followed by direct DNA electrical and mechanical characterization. In addition, our data provides a "proof-of-principle" for the feasibility of the on-chip label free DNA detection device that can be used for a variety of biomedical applications focused on sequence specific DNA detection.

The influence of the parasitic current on the nonlinear electrical response of capacitively sensed cantilever resonators

The influence of the parasitic feedthrough current on the nonlinear electrical response of capacitively sensed cantilever resonators is analyzed theoretically and experimentally. We show that the parasitic current strongly affects the shape of the nonlinear electrical frequency response of such devices. Specifically, we demonstrate that in the electrical measurement, the directions of the jumps from the different transitions between branches of stable solutions depend on the parasitic current and are independent of the jumps directions in the mechanical domain. As a consequence, the nonlinear electrical frequency response of cantilevers with capacitive readout presents three different hysteretic cycle topologies: counterclockwise, bow tie, and clockwise. This is in contrast with the only one topology (counterclockwise) that appears in the nonlinear mechanical frequency response.

The development of a method for crack-depth estimation in concrete by the electric response parameters to pulse mechanical excitation

A method is proposed for contactless testing of cracks in concrete by the electric response parameters to pulse mechanical excitation. Theoretical research is conducted on the electric response to pulsed elastic impact of the material with piezoelectric quartz inclusions. Numerical results are confirmed by experimental research on concrete samples. It is shown that the presence and growth of a crack in concrete lead to a change in measured electrical signal frequency response. Increase in crack depth leads to a shift of dominant spectral peaks to the lower-frequency region and decreases the cross-correlation coefficient between spectra from the sample containing defects and a solid sample.

Ultrasound velocity mapping with Lorentz force hydrophone

In previous work [Grasland-Mongrain et al. 2013], a Lorentz force hydrophone consisting of a cylindrical arrangement of magnets around a thin metallic wire has been presented. An ultrasonic wave vibrates the wire inside a magnetic field, which induces an electrical current. The ultrasound velocity map is then tomographically reconstructed by recording the current amplitude after translation and rotation of the wire. A hydrodynamic model provides a relationship between the velocity and the measured tension. Wire tension influence, electrical output characteristics, frequency response, sensitivity, directionality, and robustness to cavitation were characterized. A multi-wires hydrophone was also fabricated and tested. Results show that tension of the wire has negligible influence on the signal. No peak of electrical impedance was observed from 0.15 to 10 MHz. The signal was linear over pressure from 50 kPa to 15 MPa. The hydrophone was robust even when cavitation activity occurred. The directivity is explained with the Lorentz force expression. The multi-wire hydrophone could work only at low frequencies. Such hydrophone could be of interest for high intensity acoustic field characterization.

Physically based analysis of electrical frequency response of passive microelectronic circuits by heterodyne lock-in thermal means

This paper combines the heterodyne modulation technique with lock-in detection approaches to characterize the electrical behaviour of electronic systems in the frequency domain by thermal means. A thermal test chip (TTC), featuring a heating resistor and an embedded thermal sensor, is used as a test vehicle to assess this approach. The frequency response of the heating resistor has been first characterized by electrical measurements, yielding to a suitable TTC equivalent circuit which qualitatively explains its behaviour. Then, in order to infer this behaviour by thermal means, the heating resistor temperature has been heterodynally detected by on-chip local sensing (embedded thermal sensor) and off-chip spatially resolved (infrared lock-in thermography) techniques. The results of this paper show that from low-frequency temperature measurements it is possible to obtain the electrical frequency response of the TTC and to detect and locate capacitive coupling that disturbs the high-frequency operation of the device.

Parametric study of laterally acoustically coupled bulk acoustic wave filters

Acoustically coupled thin-film bulk acoustic wave resonator filters, in which the coupling takes place mechanically in the lateral direction between closely-spaced narrow resonators, are a promising approach to passband filtering at gigahertz frequencies. In this paper, filters with interdigital electrode structures are studied. Electrode number, electrode width, and coupling gap width are varied. The resonators are solidly mounted, having an acoustic mirror isolating the resonator from a Si substrate and providing the means to engineer the acoustic dispersion properties of the resonators. The center frequency of the filters is around 2 GHz. Electrical frequency responses of the filters are measured and the strength of the lateral acoustic coupling is calculated from the measurements. The effects of device parameters on the acoustic coupling and the obtainable filter bandwidth are analyzed in detail. A bandpass filter with 4.9% bandwidth, minimum insertion loss of 2 dB and sharp transition from passband to suppression band, is presented.

Concurrent attenuation of, and energy harvesting from, surface vibrations: experimental verification and model validation

Fundamental studies in vibrational energy harvesting consider the electromechanically coupled devices to be excited by uniform base vibration. Since many harvester devices are mass–spring systems, there is a clear opportunity to exploit the mechanical resonance in a fashion identical to tuned mass dampers to simultaneously suppress the vibration of the host structure via reactive forces while converting the ‘absorbed’ vibration into electrical power. This paper presents a general analytical model for the coupled electro-elastic dynamics of a vibrating panel to which distributed energy harvesting devices are attached. One such device is described which employs a corrugated piezoelectric spring layer. The model is validated by comparison to measured elastic and electric frequency response functions. Tests on an excited panel show that the device, contributing 1% additional mass to the structure, concurrently attenuates the lowest panel mode accelerance by >20 dB while generating 0.441 µW for a panel drive acceleration of 3.29 m s−2. Adjustment of the load resistance connected to the piezoelectric spring layer verifies the analogy between the present harvester device and an electromechanically stiffened and damped vibration absorber. The results show that maximum vibration suppression and energy harvesting objectives occur for nearly the same load resistance in the harvester circuit.

Effect of geometry on the performance of MEMS aluminum nitride trampoline resonators in longitudinal resonance

The performance of a microscale aluminum nitride piezoelectric resonator in the shape of a trampoline is analyzed using three-dimensional finite element simulations. The air-suspended resonator is supported by beams and is designed to respond to longitudinal through-thickness vibrations. The device is targeted to operate at UHF frequencies (3GHz) suitable for wireless filtering applications. Energy loss due to material damping is accounted for in the model. Other sources of damping are considered. We analyze if and how the material thickness, number of beams and beam length affect the resonator performance. This is intended to provide useful information at the design stages and eliminate the high costs associated with manufacturing a filter with poor performance. Performance is evaluated by means of the electromechanical coupling coefficient (K2) and the quality factor (Q) calculated from the electrical impedance frequency response plots. The results indicate that (i) K2 is insensitive to geometry (K2∼6.5%), (ii) Q increases linearly with the AlN thickness attaining Q∼1900 for a 1.7μm thick resonator and (iii) a trampoline resonator with three beams has a better performance capability than the resonator with four or eight beams with a figure of merit K2Q∼120 and resonating at a higher frequency value than its counterparts resonators, peaking at 3.21GHz. The performance figures agree well with those predicted by a one dimensional theory. The value of K2 also agrees well with test data but that of Q is higher than the one recorded in the lab.

Analytical and experimental comparisons of electromechanical vibration response of a piezoelectric bimorph beam for power harvesting

Power harvesters that extract energy from vibrating systems via piezoelectric transduction show strong potential for powering smart wireless sensor devices in applications of health condition monitoring of rotating machinery and structures. This paper presents an analytical method for modelling an electromechanical piezoelectric bimorph beam with tip mass under two input base transverse and longitudinal excitations. The Euler–Bernoulli beam equations were used to model the piezoelectric bimorph beam. The polarity-electric field of the piezoelectric element is excited by the strain field caused by base input excitation, resulting in electrical charge. The governing electromechanical dynamic equations were derived analytically using the weak form of the Hamiltonian principle to obtain the constitutive equations. Three constitutive electromechanical dynamic equations based on independent coefficients of virtual displacement vectors were formulated and then further modelled using the normalised Ritz eigenfunction series. The electromechanical formulations include both the series and parallel connections of the piezoelectric bimorph. The multi-mode frequency response functions (FRFs) under varying electrical load resistance were formulated using Laplace transformation for the multi-input mechanical vibrations to provide the multi-output dynamic displacement, velocity, voltage, current and power. The experimental and theoretical validations reduced for the single mode system were shown to provide reasonable predictions. The model results from polar base excitation for off-axis input motions were validated with experimental results showing the change to the electrical power frequency response amplitude as a function of excitation angle, with relevance for practical implementation.

TCAD modeling of NPN-SI-BJT electrical performance improvement through SiGe extrinsic stress layer

The impact of introducing a SiGe stress layer formed over the extrinsic base and adjacent to the intrinsic base of NPN-Si-BJT device on the electrical properties and frequency response has been studied using TCAD modeling. Approximately 42% improvement in f t and 13% improvement in f max have been achieved for the strained NPN-Si-BJT device in comparison with an equivalent standard conventional BJT device. In addition to that, an enhancement of the collector current by almost three times has been achieved. The same approach has been applied for NPN-SiGe-HBT device to clarify the impact of the extrinsic SiGe stress on the device's performance using TCAD modeling. Simulation results have shown that applying the SiGe stress layer on the base region of the HBT device is less efficient in comparison with the BJT device, as the SiGe base is already stressed due to the existence of Ge at the base. Approximately 5% improvement in f max and 3% improvement in f t have been achieved for the strained HBT device in comparison with an equivalent standard conventional HBT device.

Dual-mode IVUS catheter for intracranial image-guided hyperthermia: feasibility study.

In this study, we investigated the feasibility of modifying 3-Fr IVUS catheters in several designs to potentially achieve minimally-invasive, endovascular access for image-guided ultrasound hyperthermia treatment of tumors in the brain. Using a plane wave approximation, target frequencies of 8.7 and 3.5 MHz were considered optimal for heating at depths (tumor sizes) of 1 and 2.5 cm, respectively. First, a 3.5-Fr IVUS catheter with a 0.7-mm diameter transducer (30 MHz nominal frequency) was driven at 8.6 MHz. Second, for a low-frequency design, a 220-μm-thick, 0.35 x 0.35-mm PZT-4 transducer--driven at width-mode resonance of 3.85 MHz--replaced a 40-MHz element in a 3.5-Fr coronary imaging catheter. Third, a 5 x 0.5-mm PZT-4 transducer was evaluated as the largest aperture geometry possible for a flexible 3-Fr IVUS catheter. Beam plots and on-axis heating profiles were simulated for each aperture, and test transducers were fabricated. The electrical impedance, impulse response, frequency response, maximum intensity, and mechanical index were measured to assess performance. For the 5 x 0.5-mm transducer, this testing also included mechanically scanning and reconstructing an image of a 2.5-cm-diameter cyst phantom as a preliminary measure of imaging potential.

Optical DQPSK System Performance Evaluation Using Equivalent Differential Phase in Presence of Receiver Imperfections

The performance evaluation of optical differential quadrature phase-shift keying (DQPSK) systems through numerical simulation using a Gaussian approach (GA) for the equivalent differential phase (EDP) statistics is analyzed. It is shown that the GA describes quite accurately the probability density function (PDF) of EDP for a large range of DQPSK receiver (RX) imperfections. A semi-analytical simulation method (SASM) for bit error probability (BEP) evaluation based on the GA for the EDP is derived, proving to be quite accurate in presence of RX imperfections. The SASM takes into account the signal-noise beat variance dependence on signal waveform distortion and arbitrary optical and electrical filtering frequency responses. Closed-form expressions for the mean and standard deviation of EDP are derived which allows evaluating the DQPSK system performance in a quite time-efficient manner. Discrepancies not exceeding 0.1 dB on the optical SNR penalty estimated by the SASM for a BEP of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> when compared with Monte Carlo simulation are observed for the majority of the acceptable RX imperfections. Only the time-misalignment of the signals at the balanced detector input leads to higher discrepancies but not exceeding 0.3 dB even for considerable time-misalignment.

Zero-level packaging of MEMS in standard CMOS technology

A novel technique for global packaging of MEMS devices using standard CMOS technology is presented. A MEMS polysilicon resonator is fabricated and on-chip packaged using two metal layers already available from the CMOS technology. A simple buffered HF wet etching process is performed in house to release the MEMS resonator while metal deposition is used to vacuum seal the zero-level package. Both post-processing steps are carried out on CMOS chips. The design of the metal layers is carefully done in order to avoid the degradation of the MEMS. The electrical frequency response of the resonator is used for testing the performance of the final package. Electrical measurements and physical characterization demonstrate proper performance of the MEMS resonator and package.

Analysis of Piezoelectric Ultrasonic Transducers Attached to Waveguides Using Waveguide Finite Elements

A finite-element modeling procedure for computing the frequency response of piezoelectric transducers attached to infinite constant cross-section waveguides, as encountered in guided wave ultrasonic inspection, is presented. Two-dimensional waveguide finite elements are used to model the waveguide. Conventional three-dimensional finite elements are used to model the piezoelectric transducer. The harmonic forced response of the waveguide is used to obtain a dynamic stiffness matrix (complex and frequency dependent), which represents the waveguide in the transducer model. The electrical and mechanical frequency response of the transducer, attached to the waveguide, can then be computed. The forces applied to the waveguide are calculated and are used to determine the amplitude of each mode excited in the waveguide. The method is highly efficient compared to time integration of a conventional finite-element model of a length of waveguide. In addition, the method provides information about each mode that is excited in the waveguide. The method is demonstrated by modeling a sandwich piezoelectric transducer exciting a waveguide of rectangular cross section, although it could be applied to more complex situations. It is expected that the modeling method will be useful during the optimization of piezoelectric transducers for exciting specific wave propagation modes in waveguides.

A short carrier lifetime semiconductor optical amplifier with n-type modulation-doped multiple quantum well structure

Semiconductor optical amplifiers (SOAs) with n-type modulation-doped multiple quantum well structure have been investigated. The shortened carrier lifetime is derived from the PL spectrum and electrical modulation frequency response measurement. The carrier lifetime in semiconductor optical amplifiers with any n-type-2-modulated doping multiple quantum well structure is less than 60% of that in the undoped partner. The shortest measured carrier lifetime of 236 ps in the MD-MQW SOA with sheet carrier density of 3 × 1012 cm−2 was only 38% of that in the undoped MQW SOA, which can increase the wavelength conversion efficiency via four wave mixing by a factor of about 7 and switching speed via XGM and XPM applications by a factor of 2.63.

Study of electrical frequency response through the metal-insulator transition in highly conducting polymers

Based on a random resistor network (RRN), we study the electrical frequency response, including the unusual frequency dependent conductivity and multiple zero crossing of the dielectric function of highly conducting polymers. The electronic transport properties can be studied by modeling the system as a chain-linked granular network, with metallic regions randomly distributed in an amorphous host. Taking into account the contributions of coherent and incoherent transport channels, and the percolation effect of conducting polymers in our RRN model, we can well explain the negative value of ε and the low-energy structure of conducting polymers. The calculated ε(ω) and σ(ω) reproduce the main features of recent broadband optical experiments.

Frequency response of strain-compensated InGaAsN-GaAsP-GaAs SQW lasers

We investigate the below and above threshold frequency response of InGaAsN lasers with different nitrogen content. This is accomplished through detailed analysis of the small signal modulation response of the laser diodes using a comprehensive model based on rate equations and that incorporates the effect of parasitics. For below threshold conditions the model is instrumental in separating the contributions from the parasitics (more severe at low bias) and carrier recombination (predominant at higher bias) to the measured carrier lifetime. It is found that the addition of nitrogen reduces the recombination lifetime, mainly as a result of a four-fold increase in monomolecular recombination which predominates even near threshold. For bias above threshold the analysis compares electrical versus optical modulation frequency responses and concludes that resonance frequency and damping extracted from the electrical modulation responses are significantly influenced by the device parasitics. Instead, it is shown that optical modulation traces allow extraction of a relaxation frequency that is shaped only by the stimulated processes in the laser active region. Even in this case, the damping is found to be affected by the parasitics. When compared with nitrogen free lasers, a reduction in the resonance frequency is observed, while the damping is not altered. The former arises from a factor of /spl sim/2.5 decrease in the combined effect of the differential gain and carrier transport parameters. The latter reflects the more significant contribution of the parasitics to the damping.

Electrooptic Crystal Multiplier Based on Two Cascaded Pockels Crystals

A novel electrooptic crystal multiplier is proposed which can perform voltage multiplication by using two cascaded Pockels crystals with different polarization azimuths. Different from a conventional analog multiplier, the novel crystal-based multiplier allows us to modulate light wave by voltage product signal, and to obtain the voltage product signal from the measurement of light intensity. Thus, this multiplier possesses electrical insulation property and broad-band frequency response characteristics. The primary experimental result has demonstrated the feasibility of this crystal-based multiplier and its four-quadrant multiplication performance.

Finite element simulation for a new disc-type ultrasonic stator.

This paper is concerned with the development of a new disc-type piezoelectric ultrasonic stator. Linear piezoelectric, mechanical, and piezoelectro-mechanic behaviors of a metal disc structure embedded with piezoelectric actuator are considered. Using a finite element method, a dynamic formulary is modeled for the new disc-type piezoelectric ultrasonic stator. In this model, a 3-dimensional (D) mechanical element with an extra electrical degree of freedom is used to simulate dynamic vibration modes and analyze characteristic responses such as electrical impedance response, phase response, and mechanical frequency response for a new disc-type piezoelectric ultrasonic stator. An adaptive boundary condition, simple support condition with three nonequal-triangular fixed points near the edge for the mechanism design of a new disc-type piezoelectric ultrasonic stator is defined so that a lateral elliptical motion of the contact point between stator and rotor can be realized for driving the rotor. The finite element results have been compared with the experimental measurements. As a result, the analysis model seems to be similar to the real condition.